Re: is Vax addressing sane today

On Fri, 4 Oct 2024 7:05:34 +0000, Anton Ertl wrote:

George Neuner <gneuner2@comcast.net> writes:

<snipping>

>
I don't agree with all of that, however.  E.g., when discussing a VAX
instruction similar to IA-32's REP MOVS, he considers it to be a big
advantage that the operands of REP MOVS are in registers.  That
appears wrong to me; you either have to keep REP MOVS in decoding (and
thus stop decoding any later instructions) until you know the value of
that register coming out of the OoO engine, making REP MOVS a mostly
serializing instruction.  Or you have a separate OoO logic for REP
MOVS that keeps generating loads and stores inside the OoO engine.  If
you have the latter in the VAX, it does not make much difference if
the operand is on a register or memory.  The possibility of trapping
during REP MOVS (or the VAX variant) complicates things, though: the
first part of the REP MOVS has to be committed, and the registers
written to the architectural state, and then execution has to start
again with the REP MOVS.  Does not seem much harder on the VAX to me,
however.

My 66000 has a MemMove instruction consisting of a 1 word instruction,
that leaves DECODE and enters into one MEMory unit, where it proceeds
to AGEN and Read, AGEN and Write, leaving the rest of the function
units proceeding to whatever is next.
One thing I did different, here, none of the 3 registers is modified,
yet I retain the ability to take exception and re-play the instruction
from where it left off {in state never visible to the instruction
stream except via DECODE stage.}

- anton